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Low noise props
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<blockquote data-quote="Gryphon962" data-source="post: 90350" data-attributes="member: 17283"><p>Given near-silent motors, the biggest factor contributing to noise is rotor rpm. Two quads of same weight, one with regular blades, another with more efficient ones, will show a clear difference in noise level as the regular blades have to turn faster to achieve same lift. Caveat - noise levels as perceived by humans are subjective: higher frequencies (high rotor rpm) are perceived as more noisy than lower frequencies (lower rpm) <em>even if the db level when measured is the same.</em></p><p></p><p>Supersonic tip speeds are what limits the speeds of conventional helicopters (along with retreating blade stall). I havent done the math, but I very much doubt that tip speeds of any small drone are hitting 330 m/s or thereabouts. EDIT: I did the math (30,000 rpm = 500 rev/sec = 3142 rad/sec, so a 10 cm blade turning at 30 krpm would be at 314 m/sec tip speed and be transonic in forward flight at 15 m/sec).</p><p></p><p>So when it comes to aftermarket props, we have to start with the assumption that DJI picked the optimum airfoil for the stock blades such that at max collective the current draw equals the rating of the power supply system. If you fit props with airfoils that move more air, you will hover at lower rpm and expect lower noise levels (perceived) but will be able to overstress the power supply if you give it full beans. So, if your drone has aftermarket props and you get power warnings at full power, you should have a quieter drone in the hover than it was stock.</p></blockquote><p></p>
[QUOTE="Gryphon962, post: 90350, member: 17283"] Given near-silent motors, the biggest factor contributing to noise is rotor rpm. Two quads of same weight, one with regular blades, another with more efficient ones, will show a clear difference in noise level as the regular blades have to turn faster to achieve same lift. Caveat - noise levels as perceived by humans are subjective: higher frequencies (high rotor rpm) are perceived as more noisy than lower frequencies (lower rpm) [I]even if the db level when measured is the same.[/I] Supersonic tip speeds are what limits the speeds of conventional helicopters (along with retreating blade stall). I havent done the math, but I very much doubt that tip speeds of any small drone are hitting 330 m/s or thereabouts. EDIT: I did the math (30,000 rpm = 500 rev/sec = 3142 rad/sec, so a 10 cm blade turning at 30 krpm would be at 314 m/sec tip speed and be transonic in forward flight at 15 m/sec). So when it comes to aftermarket props, we have to start with the assumption that DJI picked the optimum airfoil for the stock blades such that at max collective the current draw equals the rating of the power supply system. If you fit props with airfoils that move more air, you will hover at lower rpm and expect lower noise levels (perceived) but will be able to overstress the power supply if you give it full beans. So, if your drone has aftermarket props and you get power warnings at full power, you should have a quieter drone in the hover than it was stock. [/QUOTE]
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Low noise props